1. Field of the Invention
The present invention relates to a power source device, an electronic device, an image forming apparatus, and a power source control method.
2. Description of the Related Art
Recently, for the purpose of power saving, an electronic device such as an image forming apparatus that includes a power saving mode (also known as a sleep mode) to reduce the power consumption in a stand-by state, has been widely known.
Specifically, this kind of an electronic device has a power source device that includes a first voltage generating unit (a 24 V generating unit) to supply a first voltage of 24 V, for example, to a load of a drive system such as a motor based on the power supplied from a power source (utility power) and a second voltage generating unit (a 5 V generating unit) to supply a second voltage of 5 V, for example, to a load of a control system such as a control unit based on the power supplied from the power source. In the electronic device, during normal operation when not in the power saving mode, voltage is supplied to the load in the drive system by the first voltage generating unit and to the load in the control system by the second voltage generating unit. When shift to the power saving mode takes place, the power supplied from the power source to the first voltage generating unit is shut off to stop the action of the load in the drive system, thereby enabling only the load in the control system to operate by the voltage supplied from the second voltage generating unit.
In this kind of an electronic device, if the voltage supplied to the load in the drive system and the load in the control system is reduced due to an unexpected instantaneous power interruption (for at least 10 ms), trouble in an image forming operation may occur. For that reason, the electronic device includes, in each of the first voltage generating unit and the second voltage generating unit in the direct current (DC) power source device, an electrolytic capacitor (power storage unit) to store electrical charge (power) based on the power supplied from the power source, whereby stable voltage is supplied to the loads using the electrical charge stored in the electrolytic capacitors if an instantaneous power interruption occurs.
However, in this kind of an electronic device, when the voltages supplied to the first voltage generating unit (24 VDC) and the second voltage generating unit (5 VDC) are shut off, for example, by turning off a power switch (SW), the voltage (5 V) supplied to the load in the control system is reduced earlier than the voltage (24 V) supplied to the load in the drive system because more electrical charge has been stored to the electrolytic capacitor of the first voltage generating unit than the electrolytic capacitor of the second voltage generating unit. As a result, a problem such as an erroneous operation may occur.
In the related art, a technology that can solve the problem described above has been known in which an electric discharge circuit is provided at the load in the drive system to accelerate discharging of the voltage supplied to the load in the drive system; the voltage supplied to the load in the drive system is reduced to the level equal to or less than a predetermined voltage to prevent occurrence of erroneous operation, using the electric discharge circuit; and If the voltage has been lowered to the level equal to or less than the predetermined voltage, discharging using the electric discharge circuit is stopped (refer to Japanese Patent Application Laid-open No. 2002-258687, for example).
However, in the technology disclosed in Japanese Patent Application Laid-open No. 2002-258687, a configuration in which the power remaining in the storage unit such as the electrolytic capacitor is wasted using the electric discharge circuit is employed. There is a problem from the viewpoint of saving resources and energy.
There is a need to provide a power source device, an electronic device, an image forming apparatus, and a power source control method capable of achieving resource saving and energy saving by effectively utilizing the power remaining in a storage unit rather than wasting the power.